Keep expression when normalizing is_struct in blame

Closes #12243.

Author: josevalim

lib/elixir/lib/exception.ex

@@ -291,13 +291,11 @@ defmodule Exception do
     end
   end
 
-  defp undo_is_struct_guard(
-         {:and, meta, [_, %{node: {_, _, [{_, _, [_, {struct, _, _}]} | optional]}}]}
-       ) do
+  defp undo_is_struct_guard({:and, meta, [_, %{node: {_, _, [{_, _, [_, arg]} | optional]}}]}) do
     args =
       case optional do
-        [] -> [{struct, meta, nil}]
-        [module] -> [{struct, meta, nil}, module]
+        [] -> [arg]
+        [module] -> [arg, module]
       end
 
     %{match?: meta[:value], node: {:is_struct, meta, args}}

lib/elixir/test/elixir/exception_test.exs

@@ -428,6 +428,8 @@ defmodule ExceptionTest do
               when is_binary(url) or (is_struct(url) and is_struct(url, url_module) and false) do
             url
           end
+
+          def sub_get!(url) when is_struct(url.sub, URI), do: url.sub
         end
       )
 
@@ -477,6 +479,19 @@ defmodule ExceptionTest do
 
                  def get!(url) when -is_binary(url)- or is_struct(url) and is_struct(url, URI) and -false-
              """
+
+      assert blame_message(Req, & &1.sub_get!(%{})) =~ """
+             no function clause matching in ExceptionTest.Req.sub_get!/1
+
+             The following arguments were given to ExceptionTest.Req.sub_get!/1:
+
+                 # 1
+                 %{}
+
+             Attempted function clauses (showing 1 out of 1):
+
+                 def sub_get!(url) when -is_struct(url.sub, URI)-
+             """
     end
 
     test "annotates badarg on apply" do